1. Field of the Invention
The present invention relates to an air spring that uses pneumatic pressure and which causes the generation of elastic reactive force on an inputted load, and which supports the inputted load with this reactive force.
2. Description of the Related Art
A device such as that recited in the Official Gazette of JP-A No. 2004-156663 is known as an air spring used in applications such as vehicle suspensions. This air spring is provided with a shell (chamber component) linked to one of a support body or a movable body; a piston (piston component) linked to the other of the support body and the movable body; and a diaphragm that is formed into a cylindrical shape and whose middle portion is in a state where the inside and outside are reversed. The diaphragm has one end and another end that are respectively linked to the chamber component and the piston component, and a chamber is formed in the interior of the diaphragm.
The above-described air spring is provided with a dustcover arranged at the outer peripheral side of the diaphragm in order to protect the diaphragm from foreign matter such as rocks and sand, and from the atmosphere that includes reactive gases, such as oxygen. A linking tube is provided at the dustcover and fixed to the outer peripheral side of the chamber component at the upper end portion thereof. A shoulder portion that extends from the lower end portion of the linking tube towards the outer peripheral side is integrally provided with a tubular bellows portion that extends downward from the lower end portion of the shoulder portion and which can extend and contract along the direction of movement of the movable body. Here, the cross-sectional form of the shoulder portion is formed into a tapered shape where the inner and outer diameters widen downward towards the outer peripheral side.
The above-described air spring can be applied to vehicle suspensions. In this case, the chamber component is fixed to the vehicle side, which acts as the support body, and the piston component is linked and fixed to the suspension arm that is the movable body. The diaphragm is arranged between the vehicle body and the suspension arm in a state where it can extend and contract along the direction of pitching. Due to this, when the suspension arm pitches toward the vehicle body side (i.e., bound direction) due to load from the road surface side, the air inside the chamber in the diaphragm is compressed and the air pressure rises, and the load inputted from the road surface side through the suspension arm is supported by this air pressure. At this time, by adjusting the pressure of the air filled inside the chamber, it becomes possible to adjust the position of the suspension arm that is in a neutral position.
A dustcover such as that described above is generally formed integrally with blow-molding formation (blow-forming) using a material such as a resin or rubber and the like. Accordingly, the respective thicknesses of the linking portion, the shoulder portion, and the bellows portion cannot be greatly changed. Also, the linking portion, the shoulder portion, and the bellows portion cannot be formed from different types of materials where their respective specific intensities differ. For this reason, when forming the dustcover, it becomes difficult to make the rigidity of the shoulder portion sufficiently high when the flexibility of the bellows portion in the extending/contracting directions has been made high for the sake of ensuring good following qualities of the dustcover relative to the moving body (i.e., the suspension arm).
With the above-described air spring, when the rigidity of the shoulder portion in the dustcover is insufficient, the shoulder portion becomes unable to withstand the restorative force of the bellows portion at the time of suspension arm bounding, i.e., when the bellows portion is compression deformed. A phenomenon thus occurs where the shoulder portion deforms (i.e., flex deforms) so as to roll up towards the linking tube side. If this type of straining deformation occurs repeatedly at the shoulder portion, damage such as cracks and the like tend to occur in the shoulder portion in a relatively short period of time, and this can decrease the lifespan of the dustcover.